There is an ongoing demand for commodities in developed economies and growing demand in developing countries as a result of the industrial revolution and urbanization occurring in China, India and other countries globally. This demand leads to global exploration and development of economic concentrations of a wide variety of minerals and elements including but not limited to iron oxides for use in iron and steel making. Occurrences of iron oxides, whether present in their natural state or in tailings of prior mining or mineral processing operations, can be economically recoverable if low cost mineral processing systems, such as those based upon surface chemistry properties and magnetic properties of minerals, are developed that can isolate the iron oxides into commercially valuable concentrations. The efficient recovery of weakly magnetic or paramagnetic particles from assemblages of magnetic and non-magnetic particles would make many mineral and elemental occurrences around the planet economically viable as sources of iron, particularly if the concentration of gangue minerals such as silicon dioxide or silica can be reduced to levels below five percent (5.0%) by weight. Of particular economic interest are concentrations of iron that occur naturally in certain rock and mineral formations around the planet and iron concentrations that result from the creation of reject tailings deposition basins or lean ore stockpiles resulting from past mining and mineral processing operations. These tailings basins and stockpiles represent a collection of elements in a form that already has considerable energy, manpower and “carbon footprint” invested into the mining and size reduction of the rock involved and therefore such occurrences have even greater economic and environmental attraction in the ongoing search for low cost commodities and concerns regarding environmental impacts and climate change. However, to date mineral processing systems that can cost effectively and with nominal environmental impact isolate iron oxides from gangue minerals and selectively concentrate the iron mineral assemblages such that gangue minerals such as silica are reduced to levels below 5% by weight are needed.
Processes in the prior art for refining hematite by silica removal from near final concentrates typically have operated at pH levels above 9.0 and usually above 10.0. Achieving these high pH levels requires expensive reagents and conditioners and the use of the necessary reagents and conditioners can negatively impact the environment where such processes are performed. There is an ongoing need, therefore, for advancements relating to the recovery of iron oxide concentrates and, in particular, for reducing the silica content of such concentrates. The present application addresses this need and describes methods, systems and processes that achieve significant silica removal while maintaining high iron recoveries from iron oxide-containing slurries while operating at significantly lower pH, consuming less expensive reagents, reducing costs, and consequently having less negative environmental impacts than processes employed in the prior art. As a result, the methods, systems and processes described herein are significantly more likely to be widely accepted and significantly more likely to be granted permits from regulatory authorities.